Artykuły w czasopismach na temat „Refraction”
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Aldridge, David F., i Douglas W. Oldenburg. "Refractor imaging using an automated wavefront reconstruction method". GEOPHYSICS 57, nr 3 (marzec 1992): 378–85. http://dx.doi.org/10.1190/1.1443252.
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The classical wavefront method for interpreting seismic refraction arrival times is implemented on a digital computer. Modern finite‐difference propagation algorithms are used to downward continue recorded refraction arrival times through a near‐surface heterogeneous velocity structure. Two such subsurface traveltime fields need to be reconstructed from the arrivals observed on a forward and reverse geophone spread. The locus of a shallow refracting horizon is then defined by a simple imaging condition involving the reciprocal time (the traveltime between source positions at either end of the spread). Refractor velocity is estimated in a subsequent step by calculating the directional derivative of the reconstructed subsurface wavefronts along the imaged interface. The principle limitation of the technique arises from imprecise knowledge of the overburden velocity distribution. This velocity information must be obtained from uphole times, direct and reflected arrivals, shallow refractions, and borehole data. Analysis of synthetic data examples indicates that the technique can accurately image both synclinal and anticlinal structures. Finally, the method is tested, apparently successfully, on a shallow refraction data‐set acquired at an archeological site in western Crete.
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Boengas, Sawitri, i Rivan Virlando Suryadinata. "Perbedaan Hasil Pemeriksaan Tajam Penglihatan dan Refraksi pada Anak Usia 4-12 tahun pada Pemeriksaan Non Sikloplegik dan Sikloplegik". Surya Medika: Jurnal Ilmiah Ilmu Keperawatan dan Ilmu Kesehatan Masyarakat 17, nr 1 (20.12.2021): 1–6. http://dx.doi.org/10.32504/sm.v17i1.483.
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ABSTRACTBackground of Study: Globally, there are 19 million children with visual impairment, 12 million are caused by uncorrected refractive errors. Uncorrected refractive errors in children have the potential to cause amblyopia, severe visual impairment and even blindness. Refractive errors in children must receive proper management. Cycloplegic refraction is a gold standart method for children to minimize the effect of strong accommodation in childhood. The purpose of the study: to analyze the differences between the results of the visual acuity examination and refractive examination between the non-cycloplegic and the cycloplegic examination in children aged 4-12 years. Methods: This study is an analytical observational study through recording medical records of patients 4-12 y.o between November 2020-October 2021, which were carried out with non-cycloplegic and cycloplegic refraction. Data were analyzed by SPSS with WilcoxonTest. Results: There were 106 eyes of children consisting of 62(58%) boys and 44(42%) girls. Based on statistical tests, there was no difference in natural visual acuity on non-cycloplegic and cycloplegic examinations. There were differences between non-cycloplegic and cycloplegic refractions. The difference in refraction results towards the positive spherical 75(70,75%) children towards the negative spherical 21(19.81%) children, only 10(9,4%) children showed the same results between the two refractive stages. Conclusion: There was no difference in children's visual acuity between the non-cycloplegic examination and the cycloplegic examination, but there were differences in the results of non-cycloplegic and cycloplegic refraction in children aged 4-12 years. Therefore, the determination of the size of the glasses in children must be done through cycloplegic refraction.Keywords : Refraction, Cycloplegic Refraction, Visual Acquity, Children
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Mohamed, Fathimath Nestha, i Rokiah Omar. "A situational analysis of clinical refraction services in the capital city of the Maldives". Medical hypothesis discovery and innovation in ophthalmology 10, nr 4 (24.02.2022): 146–55. http://dx.doi.org/10.51329/mehdiophthal1433.
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Background: Uncorrected refractive error is a leading cause of visual impairment globally. This study aimed to determine the current state of clinical refraction services and barriers to service provision in the capital city of the Maldives.
Methods: This cross-sectional, descriptive-analytical study used a purposive sampling technique. The list of facilities providing refraction services in the city of Malé was compiled through a desk review and finalized after verification by personnel from the Ministry of Health. The availability of human resources and infrastructure was measured using a pre-coded questionnaire that also listed barriers to service provision, followed by on-site observations and subsequent data analysis.
Results: Three clinical ophthalmology departments within hospitals, two ophthalmology hospitals, and nine primary eye care centers were selected for this study. The private sector (n = 12, 85.7%) was the primary provider of refractive error services. All facilities possessed the essential equipment required for refraction. Only optometrists and ophthalmologists conducted refraction. Contact lens assessment and low vision services were not available at any facility. The number of refractions conducted in Malé annually was 145,392. Human resources and management-related factors were the major barriers to the provision of clinical refraction services (n = 21, 44.7%).
Conclusions: Accessibility to refractive error management and low vision services is needed in Malé to meet current population needs. Existing resources, including humans and equipment, require augmentation regarding service provision and enhancement. Knowledge of these barriers could lead to the upscaling of refraction services in Malé, Maldives by health policy makers.
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Ejukonemu, Barbie O. M. "Refracting The Diseased Eye". Bayero Journal of Nursing and Health Care 3, nr 2 (11.09.2022): 893–97. http://dx.doi.org/10.4314/bjnhc.v3i2.9.
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Refractive error refers to ocular refractive status where images of objects of regard do not fall on the retina in a relaxed eye - the ametropic eye. Thus, objects are perceived as blur. Refractive error is an aberration in an otherwise normal physiological phenomenon and not a disease. Uncorrected refractive errors are the second most causes of blindness after cataract and the cause of almost half of visual impairment. Clinical refraction is a careful scientific procedure employed to correct refractive error. Given that refractive error is the most common reason patients present to the eye care practitioner, a lot of attention must be given to refraction. When an irreversible eye disease co-exist with refractive error, then correction of refractive error under this circumstance; refracting the diseased eye (RDE) become very challenging and painstaking. There will be likelihood of irregularities in the transparent refractive surfaces of the eye due to disease or surgery which make refraction difficult both for the patient and the examiner. Personal clinical experience of the author who is a low vision consultant and review of related literature from textbooks and journals are brought to bear in this article. This paper is a review of the RDE algorithm with delineation of these steps to enable an effective refractive endpoint for the eye with disease. The paper will enable young Optometrists to deal with refractive error masquerading irreversible eye disease. It is also an essential reading for the low vision Optometrist in mastering the art and science of low vision refraction.
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Dent, B. "Practical 3D refraction statics". Exploration Geophysics 20, nr 2 (1989): 207. http://dx.doi.org/10.1071/eg989207.
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Analysis of refracted first breaks has traditionally assumed that the data have been collected using special geometries that enhance the results, e.g. reversed profiles with regularly spaced geophones in-line between two shots. The geometries used to collect most 3D reflection data are quite different. Thus refraction analysis to obtain statics using traditional methods requires both approximations and selection of a subset of the data. The surface-consistent method allows use of nearly all the data, thus providing the high redundancy required for statistical robustness. A large survey incorporating both a new 3D survey and older 2D lines yielded refraction statics that greatly improved the final results.The surface-consistent method assumes that the refractor can be approximated by a horizontal plane under each station. When the refracting surface is steeply dipping, this assumption may break down. The Generalized Reciprocal Method is a traditional refraction analysis technique that gives improved results for steeply-dipping refracting surfaces. The surface-consistent method can also be made less sensitive to dip by a generalization, i.e. assume a dipping plane under each station. The refracting surface between the stations can be approximated by interpolation of these planes using the "linear projection" technique. A comparison of results using the two surface-consistent methods on synthetic data generated from a model of a buried, steep-walled valley shows the superior results obtainable.
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Carpena-Torres, Carlos, Laura Batres, María Serramito i Gonzalo Carracedo. "Repeatability of Subjective Refraction in Different Age Groups". Photonics 11, nr 7 (2.07.2024): 634. http://dx.doi.org/10.3390/photonics11070634.
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Background: The purpose of this study was to assess the inter-examiner repeatability of subjective refraction across diverse age cohorts, an aspect not previously investigated. Methods: A cross-sectional, randomized study enrolled 86 participants (mean age: 37.0 ± 18.0 years), distributed into three groups: youth, non-presbyopic adults, and presbyopic adults. Each participant underwent three subjective refractions by three different optometrists on separate days. Repeatability analysis encompassed all refractive variables (M, J0, and J45). Results: There were no significant differences between optometrists in all refractive variables for either the overall sample or across age groups (p ≥ 0.05). Additionally, no correlation was found between participants’ age and the mean difference in refractive variables across optometrists (p ≥ 0.05). The 95% confidence interval of repeatability (r) for the total sample was ±0.70 D for M, ±0.29 for J0, and ±0.21 D for J45. Conclusions: Based on these findings and previous research, it is suggested to establish 95% limits of agreement of ±0.75 D for M, and between ±0.25 D and ±0.50 D for both J0 and J45 when validating new refraction systems compared to subjective refraction as the gold standard, regardless of the age of the subjects evaluated.
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Leffler, Christopher T., Martin Wilkes, Juliana Reeves i Muneera A. Mahmood. "Postoperative Refraction in the Second Eye Having Cataract Surgery". ISRN Ophthalmology 2011 (10.12.2011): 1–6. http://dx.doi.org/10.5402/2011/273923.
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Introduction. Previous cataract surgery studies assumed that first-eye predicted and observed postoperative refractions are equally important for predicting second-eye postoperative refraction. Methods. In a retrospective analysis of 173 patients having bilateral sequential phacoemulsification, multivariable linear regression was used to predict the second-eye postoperative refraction based on refractions predicted by the SRK-T formula for both eyes, the first-eye postoperative refraction, and the difference in IOL selected between eyes. Results. The first-eye observed postoperative refraction was an independent predictor of the second eye postoperative refraction () and was weighted more heavily than the first-eye predicted refraction. Compared with the SRK-T formula, this model reduced the root-mean-squared (RMS) error of the predicted refraction by 11.3%. Conclusions. The first-eye postoperative refraction is an independent predictor of the second-eye postoperative refraction. The first-eye predicted refraction is less important. These findings may be due to interocular symmetry.
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Kumar, Rajesh S., Caitlin A. Moe, Deepak Kumar, Mahalakshmi V. Rackenchath, Sathi Devi A. V., Sriharsha Nagaraj, Dionna M. Wittberg, Robert L. Stamper i Jeremy D. Keenan. "Accuracy of autorefraction in an adult Indian population". PLOS ONE 16, nr 5 (19.05.2021): e0251583. http://dx.doi.org/10.1371/journal.pone.0251583.
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Purpose Autorefractors allow non-specialists to quickly assess refractive error, and thus could be a useful component of large-scale vision screening programs. In order to better characterize the role of autorefraction for public health outreach programs in resource-limited settings, the diagnostic accuracy of two autorefractors was assessed relative to subjective refraction in an adult Indian population. Methods An optometrist refracted a series of patients aged ≥50 years at an eye clinic in Bangalore, India using the Nidek ARK-900 autorefractor first, followed by the 3nethra Royal autorefractor, and then subjective refraction. The diagnostic accuracy of each autorefractor for myopia, hyperopia, and astigmatism was assessed using subjective refraction as the reference standard, and measures of agreement between refractions were calculated. Results A total of 197 eyes in 104 individuals (mean age 63 ± 8 years, 52% female) were evaluated. Both autorefractors produced spherical equivalent estimates that were on average more hyperopic than subjective refraction, with a measurement bias of +0.16 D (95%CI +0.09 to +0.23D) for Nidek and +0.42 D (95%CI +0.28 to +0.54D) for 3nethra. When comparing pairs of measurements from autorefraction and subjective refraction, the limits of agreement were approximately ±1D for the Nidek autorefractor and ±1.75D for the 3Nethra autorefractor. The sensitivity and specificity of detecting ≥1 diopter of myopia were 94.6% (95%CI 86.8–100%) and 92.5% (95%CI 88.9–97.5%) for the Nidek, and 89.2% (95%CI 66.7–97.4) and 77.5% (95%CI 71.2–99.4%) for the 3Nethra. The accuracy of each autorefractor increased at greater levels of refractive error. Conclusions The sensitivity and specificity of the Nidek autorefractor for diagnosing refractive error among adults ≥50 years in an urban Indian clinic was sufficient for screening for visually significant refractive errors, although the relatively wide limits of agreement suggest that subjective refinement of the eyeglasses prescription would still be necessary.
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Kim, Dong Seon, Bo Hyun Park, Han Jo Kwon, Sung Who Park i Ik Soo Byon. "Predictive Accuracy of Refraction after Transscleral Fixation of Intraocular Lenses in Trabeculectomized Eyes with Glaucoma". Journal of the Korean Ophthalmological Society 64, nr 11 (15.11.2023): 1022–29. http://dx.doi.org/10.3341/jkos.2023.64.11.1022.
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Purpose: To investigate the predictive accuracy of refraction and any change in intraocular pressure (IOP) after transscleral fixation of intraocular lenses (IOLs) in trabeculectomized eyes with glaucoma.Methods: We retrospectively reviewed the medical records of glaucoma patients who underwent trabeculectomy, followed by transscleral fixation of dislocated IOLs combined with vitrectomy. The refraction predicted by the SRK/T formula and the postoperative refraction were converted into spherical equivalents. Predictive refraction accuracies were analyzed when the differences between the two values were within ± 0.5 diopters (D) and ± 1.0 D. The IOP was measured before and after surgery.Results: Eleven eyes of 11 men (mean age, 67.27 ± 10.55 years) were included. The mean axial length was 23.64 ± 1.26 mm; the mean predicted and postoperative refractions were -0.02 ± 0.46 D and -0.80 ± 0.98 D, respectively (p = 0.029). The refractive outcome was more myopic (by -0.78 ± 1.11 D) than predicted. The predictive accuracies were 36.4% and 72.7% when the differences were ± 0.5 and ± 1.0 D, respectively. The IOP did not change during follow-up (13.18 ± 4.56, 12.82 ± 5.88, and 12.73 ± 4.58 mmHg at baseline, 1 week, and 3 months, respectively).Conclusions: In trabeculectomized eyes, transscleral IOL fixation did not affect the IOP, but the refractive outcome was more myopic than predicted. This difference should be considered when choosing IOL target power.
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Ocansey, Stephen, Rufaida Amuda, Carl Halladay Abraham i Emmanuel Kwasi Abu. "Refractive error correction among urban and rural school children using two self-adjustable spectacles". BMJ Open Ophthalmology 8, nr 1 (kwiecień 2023): e001202. http://dx.doi.org/10.1136/bmjophth-2022-001202.
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ObjectiveSelf-refracting spectacles (SRSs) have different optical and mechanical designs, which may affect the refractive outcome, depending on the experience of the end user. This study compared the performance of two SRS among children in Ghana.Methods and analysisA cross-sectional study of two Alvarez variable-focus SRS designs was conducted. A total of 167 children (mean age 13.6±1.6 years) identified as having refractive error were recruited from 2465 students who underwent screening. Subjects completed self-refraction using FocusSpecs, and Adlens, autorefraction and cycloplegic subjective refraction (CSR) (gold standard). Wilcoxon signed-rank test was used to compare visual outcomes and accuracy of refraction and graphically illustrated using Bland-Altman plots.ResultsEighty (47.9%) urban and 87 (52.1%) rural children were analysed and only about one-quarter 40 (24.0%) wore spectacles. The proportion who achieved visual acuity of ≥6/7.5 with FocusSpec, Adlens, autorefraction and CSR among urban schools were 92.6%, 92.4%, 60% and 92.6%, while those in rural schools were 81.6%, 86.2%, 54.0% and 95.4%, respectively. The mean±SD spherical equivalent errors for urban and rural schools using FocusSpec, Adlens and CSR were −1.05±0.61 D, –0.97±0.58 D and −0.78±0.53 D; and −0.47±0.51 D, –0.55±0.43 D and −0.27±0.11 D, respectively. The mean differences between the two self-refraction spectacles for urban and rural schools were not statistically different (p>0.00) but differed significantly when both were compared with the gold standard (CSR) (p<0.05).ConclusionBackground and refraction experience of school children did not significantly affect self-refraction.
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FENG, LIANG, XIAO-PING LIU, JIE REN, YAN-FENG CHEN i YONG-YUAN ZHU. "COMPARISONS OF NEGATIVE REFRACTION IN LEFT-HANDED MATERIALS AND PHOTONIC CRYSTALS". International Journal of Modern Physics B 19, nr 23 (20.09.2005): 3547–61. http://dx.doi.org/10.1142/s0217979205032371.
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Using the equifrequency surfaces (EFS) to describe negative refractions in left-handed materials (LHMs) and photonic crystals (PCs), negative phase and negative group refractive indexes in LHMs were compared with positive phase and negative group refractive indexes in PCs. The refractive indexes in PCs were dependent on frequencies and incident angles of electromagnetic wave, while indexes in LHMs were constant in the left-handed region. Furthermore, the phase compensating effect resulting from the negative phase refractive index was addressed to distinguish the perfect lens made of LHMs from the superlens realized in the all angle negative refraction (AANR) region of PCs.
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COCHENER, B. "Refraction and refractive surgery". Acta Ophthalmologica 87 (wrzesień 2009): 0. http://dx.doi.org/10.1111/j.1755-3768.2009.1256.x.
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Lu, Weicong, Zisu Peng, Wenzhi Ding, Rongyuan Ji, Yuyin Tian, Chenpei Zhao i Lin Leng. "The Influence of Accommodation on Retinal Peripheral Refraction Changes in Different Measurement Areas". Journal of Ophthalmology 2023 (22.05.2023): 1–9. http://dx.doi.org/10.1155/2023/5553468.
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Background. The change in refraction caused by accommodation inevitably affects the peripheral defocus state and thus may influence the effect of retinal peripheral myopic defocus measures in myopia control. This study investigated accommodation changes in different peripheral retinas under cycloplegia to help improve myopia control. Methods. Fifty-six eyes of fifty-six myopic subjects were recruited for this prospective study. The center and peripheral retina refractions were measured using multispectral refractive topography. The subjects were divided into low-to-moderate myopia group (range: −1.25 D to −6.00 D) and high myopia group (range: −6.25 D to −9.75 D) according to spherical equivalent (SE). The compound tropicamide (0.5% tropicamide and 0.5% phenylephrine) was used to relax the accommodation. The difference between cycloplegia and non-cycloplegia peripheral retinal refraction was analyzed using the t-test. The correlation between eccentricity and changes in peripheral refraction was analyzed using Pearson’s correlation analysis. Results. The manifest refraction of the retina significantly decreased with an increase in eccentricity after cycloplegia. The annular refraction difference value at 50°–53° (ARDV 50–53) showed the largest refraction decrease of 1.31 D compared with the central retinal refraction decrease of 0.84 D. The inferior quadrantal refraction difference value had the least change compared to the other quadrants. The relative peripheral refraction (RPR) changes in refraction difference value (RDV) at 15° (RDV-15), RDV-30, and RDV-45 were less than 0.15 D. When the range of annulus narrowed to 5°, the narrower annulus showed faster change with eccentricity increase in ARDV 30–35, ARDV 35–40, ARDV 40–45, ARDV 45–50, and ARDV 50–53. The RPR was highly correlated with eccentricity (R = 0.938 and P < 0.001 ). The high myopia group had a greater hyperopic shift in the periphery than the low-to-moderate group after cycloplegia. Conclusions. Peripheral refraction showed a significant hyperopic shift after cycloplegia with an increase in eccentricity. The RPR became more hyperopic than the central refraction. The high myopia group showed more hyperopic shifts in the peripheral region. Accommodation should be taken into consideration in peripheral defocus treatment.
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Carracedo, Gonzalo, Carlos Carpena-Torres, Cristina Pastrana, Ana Privado-Aroco, María Serramito i Laura Batres. "Repeatability of Aberrometry-Based Automated Subjective Refraction in Healthy and Keratoconus Subjects". Journal of Ophthalmology 2020 (29.10.2020): 1–7. http://dx.doi.org/10.1155/2020/4831298.
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Purpose. To compare the intersession repeatability of the Eye Refract, a new instrument to perform aberrometry-based automated subjective refraction, on healthy and keratoconus subjects. Materials and Methods. A cross-sectional and randomized study was performed. A total of 64 participants were evaluated in the study, selecting one eye per participant randomly. The sample was divided into two different groups: 33 healthy subjects (38.85 ± 13.21 years) and 31 with keratoconus (37.29 ± 11.37 years). Three refractions per participant with the Eye Refract were performed on three different days, without cycloplegia. The repeatability analysis of refractive variables (M, J0, and J45), binocular corrected distance visual acuity (BCDVA), and spent time in refraction was performed in terms of repeatability (Sr), its 95% confidence interval (r), and intraclass correlation coefficient (ICC). Results. There were no statistically significant differences ( P ≥ 0.05 ) between sessions in both groups for all refractive variables (M, J0, and J45) and BCDVA. Spent time in refraction was reduced as the sessions went by ( P < 0.05 ). The Eye Refract was more repeatable for refractive errors assessment in healthy subjects (M : Sr = 0.27 D; J0 : Sr = 0.09 D; J45 : Sr = 0.06 D) compared to those with keratoconus (M : Sr = 0.65 D; J0 : Sr = 0.29 D; J45 : Sr = 0.24 D), while it was similar for BCDVA. Conclusions. The Eye Refract offered better repeatability to assess refractive errors in healthy subjects compared to those with keratoconus. Despite measurements being also consistent in keratoconus subjects, they should be treated with caution in clinical practice.
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Mezad-Koursh, Daphna, Ari Leshno, Tomer Ziv-Baran i Chaim Stolovitch. "Refractive Changes Induced by Strabismus Corrective Surgery in Adults". Journal of Ophthalmology 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/2680204.
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Purpose. To investigate refractive changes after strabismus correction procedures among adults.Methods. Retrospective chart review of adult patients who had horizontal recti muscles surgery with preoperative and postoperative cycloplegic refraction measurements. The preoperative refraction was mathematically subtracted from the postoperative refraction, and the induced refractive changes were statistically analyzed. Vector analysis was used to examine the magnitude of the toric change. The proportion of clinically significant refractive change was evaluated as well.Results. Thirty-one eyes from 22 subjects met the criteria and were included in the final analysis. A significant postoperative refractive change of the spherical equivalent towards myopia and a change of the astigmatism in the with-the-rule direction were observed. In a subset of 9 cases a third cycloplegic refraction measurement demonstrated stable refraction compared to the 1-month postoperative measurement. In 10 cases of single eye surgery, significant refractive changes were observed only in the operated side when compared to the sound eye. The induced surgical refractive change was of clinical significance (≥0.5 D) in 11 eyes of 9 patients (40.9% of patients).Conclusions. Refractive changes are a significant side effect of horizontal strabismus corrective surgery among adults. Therefore, patients should be informed about it prior to surgery and should be rerefracted in the postoperative period.
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Jiang, Jijuan, Yang Jia, Tong Wu i Yachen Gao. "Transformation from Self-Focusing to Self-Defocusing of Silver Nanoparticles". Nanomaterials 11, nr 10 (24.09.2021): 2485. http://dx.doi.org/10.3390/nano11102485.
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The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser. It was found that, the nonlinear refraction of AgNPs shows the coexistence and transformation from self-focusing to self-defocusing. Specifically, self-focusing occurs at low excitation intensity, self-defocusing occurs at high excitation intensity, and coexistence of self-focusing and self-defocusing occurs at relatively moderate excitation intensity. The experimental results were analysed and discussed in terms of third-order and fifth-order nonlinear refractive effect. Specifically, the self-focusing is caused by the positive third-order nonlinear refraction, the self-defocusing is induced by the negative fifth-order nonlinear refraction, and the transformation from the self-focusing to self-defocusing at medium excitation intensity is caused by the competition of third-order and fifth-order nonlinear refraction. Finally, the third-order refractive index and fifth-order refractive index were obtained.
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Rowsey, J. James, i Melvin L. Rubin. "Refraction problems after refractive surgery". Survey of Ophthalmology 32, nr 6 (maj 1988): 414–20. http://dx.doi.org/10.1016/0039-6257(88)90053-7.
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Wu, Zhen, Junzhou Huo, Haidong Zhang, Fan Yang, Shangqi Chen i Zhihao Feng. "Vision Measurement Method Based on Plate Glass Window Refraction Model in Tunnel Construction". Sensors 24, nr 1 (22.12.2023): 66. http://dx.doi.org/10.3390/s24010066.
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Due to the harsh environment of high humidity and dust in tunnel construction, the vision measurement system needs to be equipped with an explosion-proof glass protective cover. The refractive effect of the plate glass window invalidates the pinhole model. This paper proposes a comprehensive solution for addressing the issue of plane refraction. First, the imaging model for non-parallel plane refraction is established based on dynamic virtual focal length and the Rodriguez formula. Further, due to the failure of the epipolar constraint principle in binocular vision systems caused by plane refraction, this paper proposes the epipolar constraint model for independent refractive plane imaging. Finally, an independent refraction plane triangulation model is proposed to address the issue of triangulation failure caused by plane refraction. The RMSE of the depth of field errors in the independent refraction plane triangulation model is 2.9902 mm before correction and 0.3187 mm after correction. The RMSE of the positioning errors before and after correction are 3.5661 mm and 0.3465 mm, respectively.
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ZHANG, YONG, i A. MASCARENHAS. "TOTAL AND NEGATIVE REFRACTION OF ELECTROMAGNETIC WAVES". Modern Physics Letters B 19, nr 01n02 (20.01.2005): 21–33. http://dx.doi.org/10.1142/s0217984905008074.
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Recently there has been a great deal of interest in an unusual category of material, that is, a material that exhibits negative refractive index or more generally negative group velocity. Perhaps the most immediate application of this type of material is in an area known as total and negative refraction, which may potentially lead to many novel optical devices. The reason that the phenomenon of total and negative refraction has become so interesting to the physics community is also due largely to the notion that this phenomenon would never occur in conventional materials with positive refractive index. It turns out that total and negative refraction can be realized even in natural crystalline materials or in artificial materials (e.g. photonic crystals) without negative (effective) refractive index. In this brief review, after providing a brief historic account for the research related to finding materials with negative group velocity and achieving negative refraction, we discuss the three primary approaches that have yielded experimental demonstrations of negative refraction, in an effort to clarify the underlying physics involved with each approach. A brief discussion on the subwavelength resolution application of the negative (effective) refractive index material is also given.
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Lee, Ji Hye, i Yang Kyung Cho. "Assessing Refractive Stability after Cataract Surgery in Axial Myopes: One-piece and Three-piece Intraocular Lenses". Journal of the Korean Ophthalmological Society 63, nr 2 (15.02.2022): 150–59. http://dx.doi.org/10.3341/jkos.2022.63.2.150.
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Purpose: To assess the refractive changes and stability after cataract surgery with insertion of three different intraocular lenses in axial myopes.Methods: A retrospective analysis was performed with 44 eyes of normal axial length (22.0 mm < axial length ≤ 24.5 mm) and 49 eyes of long axial length (24.5 mm < axial length) in patients who underwent phacoemulsification and posterior chamber lens insertion. Automated keratometry examination and refraction were performed using an autorefractor keratometer; A-scan ultrasound was used to calculate target refraction. One-piece intraocular lenses (IOLs) and three-piece IOLs were inserted. At 2 and 12 months postoperatively, refraction differences relative to the target refraction (calculated using the SRK-T formula) were analyzed. The refractive changes between 2 and 12 months postoperatively were compared according to the IOL.Results: Myopic shift from the target refraction was observed with eyes of long axial length, compared with eyes of normal axial length, at 2 and 12 months postoperatively (p = 0.003, p = 0.013). For refractive stability according to IOL, there was no significant difference in eyes with normal axial length; in eyes with long axial length, three-piece IOLs showed significant refractive stability (p < 0.05).Conclusions: In eyes with long axial length, there was a significant difference in postoperative refractive stability according to the inserted IOL; three-piece IOLs showed significant refractive stability compared with one-piece IOLs.
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Alavia, Wilson, Ismael Soto i Jorge A. Lovera. "Modeling of the Refractive Index for the Systems MX+H2O, M2X+H2O, H3BO3+MX+H2O, and H3BO3+M2X+H2O. M = K+, Na+, or Li+ and X = Cl− or SO42−". Processes 9, nr 3 (15.03.2021): 525. http://dx.doi.org/10.3390/pr9030525.
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The modeling of the refractive index for binary aqueous solutions of boric acid, sodium chloride, potassium chloride, sodium sulfate, lithium sulfate, and potassium sulfate, as well as ternary aqueous solutions of boric acid in the presence of sodium sulfate, lithium sulfate, or potassium chloride, is reported. The refraction index was represented by molar refraction. It was described as the sum of solutes’ partial molar refraction and solvent molar refraction. The solutes’ partial molar refraction was estimated from the molar refraction of the binary solutions. The excess molar refraction for these systems was described with the equation of Wang et al. The polarizability of the solutes present in the studied systems was estimated using the Lorenz–Lorenz relation. The results showed the model is appropriate for describing the systems studied; the interactions of boric acid, sodium, potassium, lithium, chloride, and sulfate ions with water molecules are relevant to explain the molar refraction and refractive index, and those for the binary systems of lithium chloride and sodium chloride are also relevant the ion–ion interactions. The model is robust and presents estimation capabilities within and beyond the concentrations and temperature range studied. Therefore, the outcomes represent valuable information to understand and follow the industrial processing of natural brines.
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Agarwa, Seema, i Dhirendra Kumar Sharma. "Ultrasonic velocities and refractive indies of binary liquid mixtures of 1, 4-dioxane with 1 – alkanols (C3, C4, C6 , C8 ) at 303.15 K". International Journal of Advanced Chemistry 9, nr 2 (2.01.2022): 201. http://dx.doi.org/10.14419/ijac.v9i2.31715.
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Density (ρ), ultrasonic velocities (u) and refractive indices (n) of the binary mixture between cyclic ether with 1-propanol, 1-butanol, 1-hexanol, 1-octanol for the entire concentration range have been measured at 303.15K, furthermore, deviation in refractive indies from ideal mixture, molar refraction, deviation in molar refraction from ideal values for these mixture has also been evaluated. The deviations from ideality of the acoustical parameters are explained on the basis of molecular interaction between the component molecules in these binary liquid mixtures. The molecular refraction (Rm), excess molecular refraction ( ) and excess molar volume (VE) were calculated from the experimental data. The results are discussed in term of molecular interactions between the components of the binary mixtures.
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Kabra, Ruchi, Krupali Raol, Hemaxi Desai, Riddhi Gajjar, Deep Panchal i Rajendra P. Maurya. "Comparison of spherical equivalent determined by Sanders-Retzlaff-Kraff-II (SRK-II) formula with target post-operative final refraction in patients undergoing cataract surgery". Indian Journal of Clinical and Experimental Ophthalmology 9, nr 4 (15.12.2023): 511–15. http://dx.doi.org/10.18231/j.ijceo.2023.097.
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The most challenging subject in patient satisfaction after cataract surgery depends upon post-operative refractive outcomes. Accurately predicting post-operative refraction is necessary during the calculation of Intraocular lens (IOL) power. The Sanders-Retzlaff-Kraff (SRK) II formula is one of the few formulae being used for the calculation of IOL power. Our study is to compare the accuracy of the SRK-II formula with targeted final refraction of patients undergoing phacoemulsification. This study was performed on 102 eyes that underwent phacoemulsification. IOL power was calculated using the SRK-II formula. One and a half months after surgery, refraction was performed. Differences between actual post-operative refraction and predicted spherical equivalent was calculated and termed absolute refractive error. Paired t-test was used for comparing actual post-operative refraction and predicted spherical equivalent.The mean absolute error (MAE) of the SRK-II formula was 0.44 D (diopters) overall. The percentage of eyes within ±0.5 D of the predicted spherical equivalent was 81%. Patients having post-operative refractive error within ±1.0 D for short, average, and long axial length were 88% (P value 0.21), 92% (P value 0.0009), and 91% (P value 0.18) respectively.We found that the SRK-II formula was accurate and reliable for predicting the post-operative refractive error in eyes with normal axial lengths as the post-operative refraction is near emmetropia and is a good method for IOL power calculation with normal axial lengths.
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Müller, Jonas, Xiaoqin Chen, Arne Ohlendorf, Lihua Li i Siegfried Wahl. "Method comparison and overview of refractive measurements in children: implications for myopia management". BMJ Open Ophthalmology 9, nr 1 (marzec 2024): e001322. http://dx.doi.org/10.1136/bmjophth-2023-001322.
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ObjectiveThis study investigated the agreement between objective wavefront-based refraction and subjective refraction in myopic children. It also assessed the impact of cyclopentolate and refraction levels on the agreement.MethodsA total of 84 eyes of myopic children aged 6–13 years were included in the analysis. Non-cycloplegic and cycloplegic objective wavefront-based refraction were determined and cycloplegic subjective refraction was performed for each participant. The data were converted into spherical equivalent, J0and J45, and Bland-Altman plots were used to analyse the agreement between methods.ResultsLinear functions were used to determine the dependency between the central myopic refractive error and the difference between the method of refraction (=bias). The influence of central myopia was not clinically relevant when analysing the agreement between wavefront results with and without cyclopentolate (comparison 1). The bias for wavefront-based minus subjective spherical equivalent refraction (comparison 2) was ≤−0.50 D (95% limits of agreement −0.010 D to −1.00 D) for myopia of −4.55 D and higher when cycloplegia was used (p<0.05). When no cyclopentolate was used for the wavefront-based refraction (comparison 3), the bias of −0.50 D (95% limits of agreement −0.020 D to −0.97 D) was already reached at a myopic error of −2.97 D. Both astigmatic components showed no clinically relevant bias.ConclusionThe spherical equivalent, measured without cycloplegic agents, led to more myopic measurements when wavefront-based refraction was used. The observed bias increased with the amount of myopic refractive error for comparisons 2 and 3, which needs to be considered when interpreting wavefront-refraction data.Trial registration numberNCT05288335.
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Ojeda Pardo, F. R., O. Belette Fuentes, V. E. Quiroz Cabascango, A. P. Mosquera Urbano i E. Reyes Céspedes. "Determination of the local refraction coefficient in Cuban lateritic mineral deposits". Journal of Physics: Conference Series 2573, nr 1 (1.09.2023): 012009. http://dx.doi.org/10.1088/1742-6596/2573/1/012009.
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Abstract Much work has been done related to the characteristics of terrestrial refraction. However, very few have referred to the fluctuations of the refractive coefficient in the lower atmosphere in Cuban lateritic deposits. The objective of this research is to determine a local refraction coefficient in different climatic conditions and time of day, to increase the precision of the mineral volume calculation and to know its behavior and to analyze the influence of local refraction coefficient variations on the trigonometric leveling. The method of reciprocal simultaneous measurements of the vertical angle was applied to minimize the influence of the refractive coefficient and assess the errors committed. As results, a refraction coefficient of 0,17 was obtained, different from the 0,14 that is currently used, and that the Gaussian refraction coefficient +0,13 is not adequate to describe the refraction effects in the lower atmosphere. In conclusion, these results can be useful to better evaluate the role of refraction in topographic surveys at 1,5 m from the visual ray of the ground, in lateritic deposits on slopes greater than 20 %. The experiment on refraction showed a range of variation of KL between 0,134-0,179 near the ground on sunny days. This equates to vertical temperature gradients are 0,064-0,144 K/m during the day and 0,054 K/m after sunset.
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Anderson, Alyssa Erin, i Gordon Hensel. "Evaluating the Adequacy of the Geographic Distribution of Eye Care Professionals in Alberta". Canadian Journal of Optometry 83, nr 2 (8.06.2021): 33–38. http://dx.doi.org/10.15353/cjo.v83i2.1552.
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A refraction is one of several tests performed by optometrists and ophthalmologists to issue a patient’s prescription for glasses. In Alberta, optometrists and ophthalmologists are authorized to perform refractions and prescribe based on that refraction; however, opticians are only authorized to refract. This study investigates whether there is a public need for opticians to be licensed to perform refractions and prescribe based on that refraction based on the adequacy of the geographic distribution of eye care professionals in Alberta. To answer this question, the optometrist and ophthalmologist to population ratios for each of Alberta’s five health zones were calculated and compared to international benchmarks. Our results show that all five of Alberta’s health zones have optometrist to population ratios that either meet or exceed the 1:10,000 international benchmark, and three of the five health zones have ophthalmologist to population ratios that meet or exceed the 3:100,000 international benchmark. Based on this data, there is an adequate distribution of optometrists but an inadequate distribution of ophthalmologists in the province. However, in regard to refractions, there is no overwhelming public need for opticians to refract and prescribe based on the refraction.
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Hardiyanti, Disti, i Fatimah Dyah NA. "Correlation between Autorefractometry and Retinoscopy with Subjective Refraction in Refractive Error Patients at Dr Kariadi Hospital, Semarang". Ophthalmologica Indonesiana 47, nr 2 (30.08.2021): 46–51. http://dx.doi.org/10.35749/journal.v47i2.100302.
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Objective: Refractive errors are a major cause of visual impairment in Indonesia. In Dr. Kariadi Hospital Semarang, it is amongst the top five diagnoses within the ophthalmology department. Therefore, objective refraction is imperative for the management of refractive errors. These examinations include autorefractometry and retinoscopy. Despite the fact that retinoscopy is the gold standard, autorefractometry is more desirable as it is more sophisticated, swift, and convenient. Autorefractometry's results are expected to match results from subjective correction, therefore, reduce examination time as patient visits increase. This study aims to determine the correlation between autorefractometry and retinoscopy examination with subjective refraction.
Methods: The study design was cross-sectional. The study was conducted on 34 eyes with refractive error taken by consecutive sampling. The subjects had to meet inclusion and exclusion criteria. All subjects underwent visual acuity examination, refractive correction by autorefractometry, retinoscopy, and subjective refraction. All data were processed by using computerized formulations.
Results: Based on the demographics there were 61.8% of women and 38.2% of men with an average age of 29.7 + 9. The results of this study showed a strong correlation between autorefractometry and subjective refraction. Furthermore, retinoscopy shows a strong correlation with subjective refraction as well.
Conclusion: This study shows retinoscopy is superior to autorefractometry. However, autorefractometry is a viable replacement for patients in Dr. Kariadi Hospital Semarang.
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Jones, Glyn M., i D. B. Jovanovich. "A ray inversion method for refraction analysis". GEOPHYSICS 50, nr 11 (listopad 1985): 1701–20. http://dx.doi.org/10.1190/1.1441861.
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A new technique is presented for the inversion of head‐wave traveltimes to infer near‐surface structure. Traveltimes computed along intersecting pairs of refracted rays are used to reconstruct the shape of the first refracting horizon beneath the surface and variations in refractor velocity along this boundary. The information derived can be used as the basis for further processing, such as the calculation of near‐surface static delays. One advantage of the method is that the shape of the refractor is determined independently of the refractor velocity. With multifold coverage, rapid lateral changes in refractor geometry or velocity can be mapped. Two examples of the inversion technique are presented: one uses a synthetic data set; the other is drawn from field data shot over a deep graben filled with sediment. The results obtained using the synthetic data validate the method and support the conclusions of an error analysis, in which errors in the refractor velocity determined using receivers to the left and right of the shots are of opposite sign. The true refractor velocity therefore falls between the two sets of estimates. The refraction image obtained by inversion of the set of field data is in good agreement with a constant‐velocity reflection stack and illustrates that the ray inversion method can handle large lateral changes in refractor velocity or relief.
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Yang, Bo, Wen Hao Lian, Wen Dong Liu i Fan Si. "The Prediction of Spacecraft Disturbance Starlight Refraction and Navigation Simulation Research". Applied Mechanics and Materials 513-517 (luty 2014): 2687–93. http://dx.doi.org/10.4028/www.scientific.net/amm.513-517.2687.
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The methods of starlight refraction navigation has very strict geometric requirements to starlight refraction direction, in order to capture the refraction of stars accurately, and avoid emerging the serious loss of accuracy of lost star, a forecasting method of interference refractive starlight is proposed in this paper. This method can consider all sorts of bodies under the influence of interference, and predict starlight direction that can happen refraction in the instant position of the corresponding spacecraft, so as to adjust the star sensor posture in advance for quick capture starlight refraction. At the same time, from the geometric relationships researching and analyzing the influence mechanism between refraction stars number and distribution by various interference, the influence of the simulation results show that refraction star distribute on both sides of the spacecraft orbit zonally, its number is closely related to the altitude. While through to accurately forecast on the starlight refraction direction, we can make the spacecraft navigation precision and capture refraction star speed increased by more than one times. Therefore, this paper has important value of engineering application.
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Eltagoury, Mahmoud, i Ehab Ghoneim. "Pediatric cycloplegic refraction". Medical hypothesis, discovery & innovation in optometry 4, nr 1 (4.04.2023): 25–33. http://dx.doi.org/10.51329/mehdioptometry170.
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Background: Cycloplegic refraction is an essential part of the pediatric ophthalmic assessment and is the cornerstone of strabismus evaluation. This narrative review aimed to ascertain the current scope of practice for cycloplegic refraction in the pediatric population.
Methods: An extensive literature review was conducted using ScienceDirect, PubMed/MEDLINE, Scopus, and Google Scholar databases using the following search terms: cyclopentolate, tropicamide, pediatric cycloplegia, atropine, homatropine, manual retinoscope, handheld autorefractometer, spherical errors, and no spherical errors of refraction in articles published from January 2000 to December 2022. Relevant retrieved references and practical points concerning pediatric cycloplegic refraction were summarized.
Results: Atropine has the most potent cycloplegic effect and is best used in cases of severe accommodative esotropia. Because of the unfavorable side effects and risks associated with atropine, cyclopentolate has been found to provide quite effective cycloplegia, even for moderate to severe hyperopia, and has become the standard agent for traditional pediatric cycloplegic exams. Tropicamide has also been shown to provide adequate cycloplegia while being less toxic and causing fewer side effects. Tropicamide has the fewest side effects and toxicity of all agents, while atropine has the most. Cyclopentolate is an exceptionally safe cycloplegic agent. To detect spherical and non-spherical refractive errors, refraction can be performed using a handheld autorefractometer or a manual retinoscope, as well as under general anesthesia in some cases. The optimal time to wear eyeglasses to maintain binocular vision and avoid amblyopia is also considered.
Conclusions: Accommodative power in children is at its maximum, and this interferes with reliable - assessment of refraction. Therefore, the use of cycloplegic refraction is mandatory during childhood to obtain actual refraction, which is considered the cornerstone for eyeglass prescription. Knowledge of the various cycloplegic agents used in childhood refraction is important for ophthalmologists and optometrists to obtain safe and effective cycloplegia. High refractive errors, as well as the presence of anisometropia or squint, necessitate the use of eyeglasses as early as childhood to maintain binocularity and depth perception.
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Brogan, Kerr, Charles J. M. Diaper i Alan P. Rotchford. "Cataract surgery refractive outcomes: representative standards in a National Health Service setting". British Journal of Ophthalmology 103, nr 4 (15.06.2018): 539–43. http://dx.doi.org/10.1136/bjophthalmol-2018-312209.
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Background/aimsTo report refractive outcomes from an National Health Service (NHS) cataract surgery service and assess if results meet suggested benchmark standard.MethodsDetails of all patients undergoing cataract surgery in the Southern General and New Victoria hospitals in Glasgow, UK, between November 2006 and December 2016 were prospectively entered into an electronic database. Patients were reviewed 4 weeks postoperatively in the eye clinic and underwent refraction at their local optometrist prior to this appointment. Surgically uncomplicated cases with in the bag’ non-toric intraocular lens implantation were included. Patients with previous laser refractive procedures or failing to achieve 6/12 acuity or better postoperatively were excluded. Proximity to targeted postoperative refraction was documented.ResultsOver this 10-year period, 11 083 eyes underwent cataract surgery. Of these, 8943 eyes of 6936 patients (80.69%) met the inclusion criteria and had both target and postoperative outcome refraction recorded. The mean difference between the targeted and outcome refraction was −0.07 D (SD 0.67). The mean absolute error was 0.50 D. Postoperative refraction was within 1 D of target refraction for 7938 eyes (88.76%) and within 0.50 D for 5577 eyes (62.36%).ConclusionRefractive outcomes following routine cataract surgery reported here are well within the targets recommended by the Royal College of Ophthalmologists and European guidelines, but suggest that higher cataract refractive outcome benchmark standards may not yet be a realistic expectation for all NHS units with current biometry practice.
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Magome, Kazuyoshi, Naoyuki Morishige, Akifumi Ueno, Taka-Aki Matsui i Eiichi Uchio. "Prediction of cycloplegic refraction for noninvasive screening of children for refractive error". PLOS ONE 16, nr 3 (15.03.2021): e0248494. http://dx.doi.org/10.1371/journal.pone.0248494.
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Detection of refractive error in children is crucial to avoid amblyopia and its impact on quality of life. We here performed a retrospective study in order to develop prediction models for spherical and cylinder refraction in children. The enrolled 1221 eyes of 617 children were divided into three groups: the development group (710 eyes of 359 children), the validation group (385 eyes of 194 children), and the comparison group (126 eyes of 64 children). We determined noncycloplegic and cycloplegic refraction values by autorefractometry. In addition, several noncycloplegic parameters were assessed with the use of ocular biometry. On the basis of the information obtained from the development group, we developed prediction models for cycloplegic spherical and cylinder refraction in children with the use of stepwise multiple regression analysis. The prediction formulas were validated by their application to the validation group. The similarity of noncycloplegic and predicted refraction to cycloplegic refraction in individual eyes was evaluated in the comparison group. Application of the developed prediction models for spherical and cylinder refraction to the validation group revealed that predicted refraction was significantly correlated with measured values for cycloplegic spherical refraction (R = 0.961, P < 0.001) or cylinder refraction (R = 0.894, P < 0.001). Comparison of noncycloplegic, cycloplegic, and predicted refraction in the comparison group revealed that cycloplegic spherical refraction did not differ significantly from predicted refraction but was significantly different from noncycloplegic refraction, whereas cycloplegic cylinder refraction did not differ significantly from predicted or noncycloplegic values. Our prediction models based on ocular biometry provide estimates of refraction in children similar to measured cycloplegic spherical and cylinder refraction values without the application of cycloplegic eyedrops.
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Pinheiro, Francisco Irochima, Eduardo Pereira De Azevedo, Amália Cinthia Meneses Rêgo, Irami Araújo Neto, Irami Araújo Filho i Paulo Schor. "A VIRTUAL SIMULATOR AS A TOOL FOR TEACHING REFRACTOMETRY". International Journal of Research -GRANTHAALAYAH 5, nr 10 (31.10.2017): 23–33. http://dx.doi.org/10.29121/granthaalayah.v5.i10.2017.2264.
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Significance: Several educational technological innovations are developed with the purpose of contributing to the training of future optometrists and ophthalmologists. However, very little is available for teaching refractometry. EYE REFRACTION is a simulator mobile applications (App) that works as a fast, straightforward and interactive interface tool for teaching refractometry. Purpose: Develop novel mobile application software (EYE REFRACTION) as a tool for teaching refractometry in medical schools. Methods: EYE REFRACTION software was developed by the emerging company “Ciência Ilustrada studio” incubated at “INOVA Metrópole” of the Digital Metropolis Institute of the Universidade Federal do Rio Grande do Norte, Brazil (IMD-UFRN), using the XCode 4.6.2. program (Apple Computer, Inc. Cupertino, CA, USA). This application software (App) was created for Tablets and has a fully interactive workspace, where after inserting the refraction data of the patient, the user can observe points or focal lines of the refractive errors and all the arrangements resulting from the various possible corrections. Results: After 90 days of blind and random simulations of the EYE REFRACTION App performed by volunteered ophthalmologists, six failures were detected and promptly corrected. Two were detected when refractive errors were simulated (simple myopic astigmatism), two during simulations of hypermetropic astigmatism, being one simple and the other compound, and two others during the simulation of mixed astigmatism. Conclusion: A novel App for teaching refractometry was successfully developed, where it enabled a real-time observation of refractive errors and their arrangements. The EYE REFRACTION App is currently available at Apple App Store.
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Shen, Yang, i Jie Zhang. "Refraction wavefield migration". GEOPHYSICS 85, nr 6 (22.10.2020): Q27—Q37. http://dx.doi.org/10.1190/geo2020-0141.1.
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Refraction methods are often applied to model and image near-surface velocity structures. However, near-surface imaging is very challenging, and no single method can resolve all of the land seismic problems across the world. In addition, deep interfaces are difficult to image from land reflection data due to the associated low signal-to-noise ratio. Following previous research, we have developed a refraction wavefield migration method for imaging shallow and deep interfaces via interferometry. Our method includes two steps: converting refractions into virtual reflection gathers and then applying a prestack depth migration method to produce interface images from the virtual reflection gathers. With a regular recording offset of approximately 3 km, this approach produces an image of a shallow interface within the top 1 km. If the recording offset is very long, the refractions may follow a deep path, and the result may reveal a deep interface. We determine several factors that affect the imaging results using synthetics. We also apply the novel method to one data set with regular recording offsets and another with far offsets; both cases produce sharp images, which are further verified by conventional reflection imaging. This method can be applied as a promising imaging tool when handling practical cases involving data with excessively weak or missing reflections but available refractions.
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Asiedu, Kofi, Samuel Kyei i Emmanuel Ekow Ampiah. "Autorefraction, Retinoscopy, Javal’s Rule, and Grosvenor’s Modified Javal’s Rule: The Best Predictor of Refractive Astigmatism". Journal of Ophthalmology 2016 (2016): 1–6. http://dx.doi.org/10.1155/2016/3584137.
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The aim of the study was to determine the level of agreement between Javal’s rule, autorefraction, retinoscopy, and refractive astigmatism and to determine which technique is the most suitable substitute when subjective refraction is not applicable using a clinical sample. A total of 36 subjects, 14 males and 22 females, were involved in this study. The intraclass correlation coefficients between subjective refraction, autorefraction, and retinoscopy were 0.895 and 0.989, respectively, for the spherical equivalent. The Bland-Altman 95% limits of agreement between subjective refraction and autorefraction; subjective refraction and retinoscopy; and autorefraction and retinoscopy were −2.84 to 3.58, −0.88 to 1.12, and −3.01 to 3.53, respectively, for the spherical equivalent. The intraclass correlation coefficients between spectacle total astigmatism and the following techniques were as follows: retinoscopy (0.85); autorefraction (0.92); Javal’s rule (0.82); and Grosvenor et al. version (0.85). The Bland-Altman 95% limits of agreement between subjective refraction and autorefraction; subjective refraction and retinoscopy; subjective refraction and Javal’s rule; and subjective refraction and Grosvenor et al. version were −0.87 to 1.25, −1.49 to 1.99, −0.73 to 1.93, and −0.89 to 1.7, respectively, for the total astigmatism. The study showed that autorefraction and Javal’s rule may provide a starting point for subjective refraction cylinder power determination but only retinoscopy may satisfactorily replace subjective refraction total astigmatism when subjective refraction is not applicable.
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Sriubienė, Margarita, Irena Andriuškevičiūtė i Algimantas Sinkus. "Eye Refraction Anomalies in Down Syndrome Families". Proceedings of the Latvian Academy of Sciences. Section B. Natural, Exact, and Applied Sciences. 63, nr 1-2 (1.01.2009): 5–8. http://dx.doi.org/10.2478/v10046-009-0011-z.
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Eye Refraction Anomalies in Down Syndrome Families The extra chromosomal material in Down syndrome patients causes a generalised disruption in the genetic balance. From this viewpoint, the non-specific developmental instability following aneuploidy might be also responsible for ocular anomalies in patients with Down syndrome. The aim of this study was to identify the eye refraction anomalies in families having individuals with Down syndrome. A total of 199 Down syndrome patients (average age 17.0 years), 85 their siblings (17.0 years) and 229 their parents (average age 48.9 years) underwent eye refraction examination. In Down syndrome patients ocular refractive findings as spherical equivalent were: emetropia 4.2±1.0%, hypermetropia 70.0±2.3%, and myopia 25.8±2.2%. Astigmatism was diagnosed in 42.8±1.5% of patients. Refraction could not be identified in 3.8±1.0% of patients. In the control group of siblings refractive findings as spherical equivalent were: emmetropia 51.2±3.8%, hypermetropia 39.4±3.7%, and myopia 9.4±2.2%. Astigmatism was diagnosed in 7.6±2.0% of siblings. In parents refractive findings as spherical equivalent were: emmetropia 42.8±2.3%, hypermetropia 40.2±2.3%, and myopia 17±1.8%. Astigmatism was diagnosed in 7.9±1.3% of parents. Refraction could not be identified in 1.1±0.5% of parents. Astigmatism, which is phylogenetically more recent, was found in Down syndrome patients 5.6 times more often than control siblings and 5.4 times more than in the parents group.
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Gurmizov, Е. P., К. B. Pershin, N. F. Pashinova i А. Iu Tsygankov. "Keratorefractive Surgery for Residual Refractive Error Correction in Pseudophakic Patients". Ophthalmology in Russia 17, nr 2 (23.06.2020): 209–15. http://dx.doi.org/10.18008/1816-5095-2020-2-209-215.
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Purpose. Evaluation of the visual and refractive results of additional correction using LASIK and PRK methods in patients with residual refractive error after previous cataract surgery. Patients and methods. The prospective open study included 57 patients (79 eyes) who previously underwent cataract phacoemulsification (n = 37) or refractive lensectomy (n = 42) with various IOL models implantation (2012–2017). The average age of patients was 50.8 ± 13.9 (19–79) years. Operations LASIK (91.1 %) and PRK (8.9 %) were carried out according to standard methods. In 6 cases, femtosecond laser supported by laser correction. The target refraction ranged from –0.25 to 0.25 D in most (97.5 %) cases. The follow-up period ranged from 6 to 9 months. Results. The patients were divided into groups according to the type of residual refractive error (Group 1 — myopia, group II — emmetropia and group III — hyperopia). Statistically significant differences were determined for the species of previously implanted IOLs — in group II, the frequency of monofocal IOLs was significantly higher (p < 0.05). In group II, the values of the cylindrical component of refraction were significantly higher compared with groups I and III (p < 0.05). In group I, a significant (p < 0.05) decrease in the spherical component of refraction from –1.36 ± 0.92 to –0.2 ± 0.8 D was observed. In patients of group II, there was a slight increase in the spherical component of refraction from 0 ± 0.20 to 0.25 ± 0.29 D (p > 0.05). In group III, a significant (p < 0.05) decrease was observed in the spherical component of refraction from 1.27 ± 0.69 to 0.43 ± 0.49 D. When analyzing the cylindrical component of refraction in group I, its decline was noted from –0.69 ± 0.5 to –0.38 ± 0.46 D (p > 0.05). In group II, the largest decrease in the cylindrical component was observed from –1.6 ± 1.0 to 0.03 ± 1.10 Dptr (p < 0.01). In all the studied groups, a statistically significant (p < 0.05) increase in UCFVA was revealed in the postoperative period. Indicators K1 and K2 did not significantly change. Conclusion. The high efficiency of the correction using the LASIK, PRK and femtoLASIK methods on pseudophakic eyes with the achievement of the target refraction in most of the studied cases was shown. This method can be used as an alternative to spectacle and contact correction in patients with residual refractive error after cataract phacoemulsification and refractive lensectomy with IOL implantation.
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Al-Hagan, Ola, Sherif M. Hanafy i Gerard T. Schuster. "Iterative supervirtual refraction interferometry". GEOPHYSICS 79, nr 3 (1.05.2014): Q21—Q30. http://dx.doi.org/10.1190/geo2013-0210.1.
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In refraction tomography, the low signal-to-noise ratio (S/N) can be a major obstacle in picking the first-break arrivals at the far-offset receivers. To increase the S/N, we evaluated iterative supervirtual refraction interferometry (ISVI), which is an extension of the supervirtual refraction interferometry method. In this method, supervirtual traces are computed and then iteratively reused to generate supervirtual traces with a higher S/N. Our empirical results with both synthetic and field data revealed that ISVI can significantly boost up the S/N of far-offset traces. The drawback is that using refraction events from more than one refractor can introduce unacceptable artifacts into the final traveltime versus offset curve. This problem can be avoided by careful windowing of refraction events.
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Ma, Zhao Yang, i Ben Ning Qu. "Application of Digital Image Correlation in Measuring Refraction Index of Transparent Material". Applied Mechanics and Materials 723 (styczeń 2015): 727–31. http://dx.doi.org/10.4028/www.scientific.net/amm.723.727.
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This article describes a method to measure the refraction index of transparent material by combining the characteristics of transparent material with 2D digital image correlation. The method established the relationship between refraction index and in-plane displacement of speckles using the refraction principle. In-plane displacement can be calculated by the 2D digital image correlation directly. Refractive index of PMMA were obtained by speckle patterns which were recorded by single camera. Results showed that the calculation is very close to the existing PMMA material refractive index value that proved the feasibility and the effectiveness of the method. Of course, this method also can be used to calculate the thickness of the transparent material to widen its using fields.
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Salim, Ashadi. "Analisis Data Seismik Refraksi dengan Metode Generalized-Reciprocal". ComTech: Computer, Mathematics and Engineering Applications 3, nr 1 (1.06.2012): 162. http://dx.doi.org/10.21512/comtech.v3i1.2397.
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The analysis of seismic refraction data by the generalized reciprocal method can be used for delineating undulating refractors. The forward and reverse times of arrival at different geophones with XY distance along a refraction profile, are used for calculating time depth. The seismic wave velocity in refractor may be obtained from velocity analysis function, and the depth of refractor under each geophone is obtained from time-depths function. This method has been applied at one line of seismic refraction measurement that was 440 m long with 45 geophone positions. The measurement obtained 20 m as the optimum XY-value and 2250 m/s as the velocity of seismic wave in refractor, and the undulating refractor topography with the depths varies 10.4 – 22.1 m. The optimum XY-value was obtained from approximate calculation derived from the observation, that was indicated the absent of undetected layer.
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Mahmud, Muhammad U., Umar F. Ibrahim, Mohammad Isyaku, Sadiq Hassan, Philips I. Ebisike i Rabi Y. Sani. "Correlation of axial length and corneal power with refractive status of patients with refractive error in Kano, North-Western Nigeria". International Journal of Research in Medical Sciences 12, nr 7 (29.06.2024): 2266–72. http://dx.doi.org/10.18203/2320-6012.ijrms20241870.
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Background: Uncorrected refractive errors are a major cause of blindness and low vision. Determination of the etiology is essential in planning appropriate treatment modalities. Aim of this study was to determine the correlation between axial length and corneal power with refractive status of patients with refractive error in Kano, Nigeria. Methods: Observational cross-sectional study in which 385 eligible patients were recruited. Relevant history was obtained from the patients and ocular examination was done. Objective and Subjective refraction were performed. Spherical equivalent was calculated for patients with astigmatism. Keratometric readings (k1 and k2) and measurement of axial length were taken. Data was analyzed using the statistical package for the social sciences (SPSS) version 22. Results: Statistically significant inverse association (r=-1.7, r2=56.8%, p<0.0001) was found between Spherical equivalent objective refraction and axial length of right eye. Statistically significant inverse association (r=-1.2, r2=53.3%, p<0.0001) was found between Spherical equivalent subjective refraction and axial length of right eye. Statistically significant inverse association (r=-0.5, r2=8.5%, p<0.0001) was found between spherical equivalent objective refraction and corneal power of the right eye. Statistically significant inverse association (r=-0.3, r2=6.4%, p<0.0001) was found between spherical equivalent subjective refraction and Corneal power of right eye. Negative correlation existed between axial length and corneal power but was not statistically significant (r=-0.0, p<0.4). Conclusions: The study established that axial length and corneal power are the determinants of refractive status and that axial length is a stronger determinant.
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Trofimov V., Rosanov N. N., Yang Y., Fedorov S. V., Yu J. i Veretenov N. A. "Refraction by gas inhomogeneities during laser heating of a metal". Optics and Spectroscopy 130, nr 4 (2022): 469. http://dx.doi.org/10.21883/eos.2022.04.53739.55-21.
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An analysis is made of the distribution of the refractive index near the boundary of a metal heated by laser radiation. The gradient of the refractive index of the gas, caused by the heat flux, and the distribution of the refractive index in the inhomogeneously heated gas are found. The drift of the laser beam due to the refraction of radiation in a gas is estimated, which shows an increase in the drift for narrow laser beams. Keywords: refraction in gas, gas heating, metal laser heating.
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Aggarwal, Aditya, Siddhartha Gairola, Uddeshya Upadhyay, Akshay P. Vasishta, Diwakar Rao, Aditya Goyal, Kaushik Murali, Nipun Kwatra i Mohit Jain. "Towards Automating Retinoscopy for Refractive Error Diagnosis". Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies 6, nr 3 (6.09.2022): 1–26. http://dx.doi.org/10.1145/3550283.
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Refractive error is the most common eye disorder and is the key cause behind correctable visual impairment, responsible for nearly 80% of the visual impairment in the US. Refractive error can be diagnosed using multiple methods, including subjective refraction, retinoscopy, and autorefractors. Although subjective refraction is the gold standard, it requires cooperation from the patient and hence is not suitable for infants, young children, and developmentally delayed adults. Retinoscopy is an objective refraction method that does not require any input from the patient. However, retinoscopy requires a lens kit and a trained examiner, which limits its use for mass screening. In this work, we automate retinoscopy by attaching a smartphone to a retinoscope and recording retinoscopic videos with the patient wearing a custom pair of paper frames. We develop a video processing pipeline that takes retinoscopic videos as input and estimates the net refractive error based on our proposed extension of the retinoscopy mathematical model. Our system alleviates the need for a lens kit and can be performed by an untrained examiner. In a clinical trial with 185 eyes, we achieved a sensitivity of 91.0% and specificity of 74.0% on refractive error diagnosis. Moreover, the mean absolute error of our approach was 0.75±0.67D on net refractive error estimation compared to subjective refraction measurements. Our results indicate that our approach has the potential to be used as a retinoscopy-based refractive error screening tool in real-world medical settings.
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Meiers, Dairis, Anete Kursīte i Guna Laganovska. "Refractive Outcome and Influencing Factors of Postoperative Refraction in Cataract Surgery". Acta Chirurgica Latviensis 17, nr 2 (20.12.2017): 17–20. http://dx.doi.org/10.1515/chilat-2017-0018.
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Abstract Introduction. Phacoemulsification with intraocular lens implantation provide high visual acuity after procedure, increasing quality of life and vision. The aim of procedure is to gain a target refraction, in most cases emmetropia, when a patient does not need visual correction for a distant sight (1). Although the preoperative evaluation and surgery technique has developed in the last years, it is not possible to gain the target refraction in all cases. There still are patients with high postoperative error, which means that there are influencing factors that should be identified. Aim of the Study. Aim of the study was to evaluate the refractive outcome three months after cataract surgery in Pauls Stradins Clinical University Hospital and to find out the factors that influence postoperative refraction after cataract surgery. Material and methods. Retrospective study included 43 eyes of 38 patients who underwent phacoemulsification’s cataract surgery with intraocular lens implantation and fixed A constant. Surgeries were done at PSCUH from August, 2017 till January, 2018. Data were collected at postoperative follow-up three months after surgery (postoperative refraction). The difference between data intervals was evaluated using nonparametric tests - Mann-Whitney tests. The correlations between postoperative refraction and potentially influencing factors of refractive outcome were evaluated by nonparametric correlation tests - Spearman’s rho test. Results. Of the patients enrolled in the study, whose median age was 75 years (IQR = 78-68 years), 20,9 % (n=9) were men, 51,2% (n=22) had no comorbidities, 34,9% (n=15) had one comorbidity, but two comorbidities had 14% (n=6) patients. At the time of cataract surgery 16,3% (n=7) of patients had Diabetes mellitus, but 46,5 % (n=20) had Glaucoma. The absolute error between target refraction and postoperative refraction for all cases was 0.48 ± 0.41 D (mean + standard deviation). The main aim of surgery - emmetropic eye - was achieved in 30,2 percent of cases (n=13). In the study, 69.8 percent of cases (n=30) were within ±0.50 D difference between target and final postoperative refraction, and 90.7 percent of cases (n=39) were within ±1.00 D. The study showed moderate and negative correlation between the axial length of eye and refractive outcome of cataract surgery: correlation coefficient r= -0.412 (p=0.006). The study showed week correlation between the age of patients and refractive outcome of cataract surgery r=0.091 (p=0.562). The difference between IOL power calculated using Haigis formula and IOL power of lens implanted during surgery also had a week correlation with refractive outcome r=0.033 (p=0.833). Correlations between comorbidities and refractive outcome were week and negative - in case of diabetes mellitus r= -0.127 but in case of glaucoma r= -0.13. Conclusions. Cataract surgery outcome showed high quality of this procedure because of the insignificant mean postoperative refractive error. The study did not show statistically significant correlation between refractive outcome and the age of patients, presence of diabetes mellitus or glaucoma and the difference between calculated and implanted IOL power. The study revealed moderate and negative correlation between the axial length and refractive outcome. This correlation coincides with the results of the studies previously made. The refractive outcome is worse for smaller eyes.
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Zapata-Rodríguez, Carlos J., David Pastor, Luis E. Martínez, María T. Caballero i Juan J. Miret. "Single-Polarization Double Refraction in Plasmonic Crystals: Considerations on Energy Flow". Applied Mechanics and Materials 472 (styczeń 2014): 729–33. http://dx.doi.org/10.4028/www.scientific.net/amm.472.729.
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We examined the optical properties of nanolayered metal-dielectric lattices. At subwavelength regimes, the periodic array of metallic nanofilms demonstrates nonlocality-induced double refraction, conventional positive and as well as negative. In particular, we report on energy-flow considerations concerning both refractive behaviors concurrently. Numerical simulations provide transmittance of individual beams in Ag-TiO2metamaterials under different configurations. In regimes of the effective-medium theory predicting elliptic dispersion, negative refraction may be stronger than the expected positive refraction.
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Dementiev, D. V. "Analysis of methods for determining the refraction coefficient in the atmospheric surface layer". Geodesy and Cartography 947, nr 5 (20.06.2019): 2–11. http://dx.doi.org/10.22389/0016-7126-2019-947-5-2-11.
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In the instructions for modern geodetic instruments, it is recommended to introduce an amendment for the refraction, taking into account the “standard” refraction coefficient k = 0,13÷0,2. In fact, in the surface layer of the atmosphere, the refractive index can range from –6 to 6. Various classical methods of determining refraction are analyzed. Conclusions based on experimental work made by various researchers are presented. Using the results of numerous studies of various methods for determining vertical refraction, it can be concluded that all classical (static) methods do not provide a high degree of reliability to determine the refraction. An exception is the method of determining refraction at a neutral temperature stratification of the atmosphere, when the time interval is not very long. For this reason, their practical application is extremely limited. To improve the accuracy of determining refraction, it is necessary to take into account the turbulence of the atmosphere, that is, to use dynamic measurement methods that take the fluctuations of the electromagnetic wave passing through the path into account.
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Abelman, Herven, i Shirley Abelman. "Tolerance and Nature of Residual Refraction in Symmetric Power Space as Principal Lens Powers and Meridians Change". Computational and Mathematical Methods in Medicine 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/492383.
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Unacceptable principal powers in well-centred lenses may require a toric over-refraction which differs in nature from the one where correct powers have misplaced meridians. This paper calculates residual (over) refractions and their natures. The magnitude of the power of the over-refraction serves as a general, reliable, real scalar criterion for acceptance or tolerance of lenses whose surface relative curvatures change or whose meridians are rotated and cause powers to differ. Principal powers and meridians of lenses are analogous to eigenvalues and eigenvectors of symmetric matrices, which facilitates the calculation of powers and their residuals. Geometric paths in symmetric power space link intended refractive correction and these carefully chosen, undue refractive corrections. Principal meridians alone vary along an arc of a circle centred at the origin and corresponding powers vary autonomously along select diameters of that circle in symmetric power space. Depending on the path of the power change, residual lenses different from their prescription in principal powers and meridians are pure cross-cylindrical or spherocylindrical in nature. The location of residual power in symmetric dioptric power space and its optical cross-representation characterize the lens that must be added to the compensation to attain the power in the prescription.
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Jiang, Ping, Kang Xie, Huajun Yang i Zhenhai Wu. "Negative Propagation Effects in Two-Dimensional Silicon Photonic Crystals". International Journal of Photoenergy 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/702637.
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We demonstrated negative refraction effects of light propagating in two-dimensional square and hexagonal-lattice silicon photonic crystals (PhCs). The plane wave expansion method was used to solve the complex eigenvalue problems, as well as to find dispersion curves and equal-frequency contour (EFC). The finite-difference time-domain (FDTD) method was used to simulate and visualize electromagnetic wave propagation and scattering in the PhCs. Theoretical analyses and numerical simulations are presented. Two different kinds of negative refractions, namely, all-angle negative refraction (AANR) without a negative index and negative refraction with effective negative index, have been verified and compared.
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Palmer, Derecke. "Resolving refractor ambiguities with amplitudes". GEOPHYSICS 66, nr 5 (wrzesień 2001): 1590–93. http://dx.doi.org/10.1190/1.1487104.
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Amplitudes are used to constrain refraction models. This study demonstrates that the refraction time section generated through the convolution of forward and reverse refraction traces together with a static shift facilitates the convenient recognition of amplitude variations related to changes in refractor wavespeed. For large contrasts in wavespeeds between the upper layer and the refractor, the head coefficient is approximately proportional to the ratio of the specific acoustic impedances. Since the convolution operation effectively multiplies the amplitudes of the forward and reverse arrivals, the convolved amplitudes are proportional to the square of this ratio. In general, the higher the contrast in the refractor wavespeed and/or density, the lower the amplitude. The regions recognized in the wavespeed analysis function correlate with those determined with amplitudes, thereby providing an additional constraint on inversion with model‐based approaches.
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Dyer, Alan M., i Angus H. Kirk. "A fully automated remote refraction system". Journal of Telemedicine and Telecare 6, nr 2_suppl (sierpień 2000): 16–18. http://dx.doi.org/10.1258/1357633001935806.
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Traditional methods of performing refractions depend on a trained refractionist being present with the subject and conducting an interactive form of subjective testing. A fully automated refraction system was installed in 13 optical dispensaries and after 15 months the patient and statistical information was gathered. The data from all operators were consistent and suggested a lack of operator effect on the refraction results. The mean of the SD of subjective sphere measurements was 0.2, or slightly less than a quarter dioptre, which would be an acceptable level of accuracy for ordering corrective lenses. The present study suggests an absence of operator influence on the results of the refractions and a degree of consistency and accuracy compatible with the prescription of lenses.